What that means is that gravity, at the quantum level, must be conveyed by a spin-2 particle, known as a ‘graviton’. It has not been detected, and probably neve

What that means is that gravity, at the quantum level, must be conveyed by a spin-2 particle, known as a ‘graviton’. It has not been detected, and probably never will be (due to technical limitations). We can broadly pin down its properties, but we do not yet have a full theory of how it interacts.